Introduce @raw_return Decorator and Upgrade Default EVM to Prague

v0.4.3 adds the @raw_return decorator allowing contracts to return bytes directly, bypassing ABI-encoding, enabling advanced proxy contract use cases. Default EVM version updated to prague. Venom optimizer pipeline improved. Contributors @gap-editor and @crypdoughdoteth made first commits (#4680, #4641). Full changelog spans v0.4.2 to v0.4.3. Details at vyperlang.org release notes.